[Accidental anesthetic overdose caused by anesthesia respirators Servo 900 C and D]

When working with the anaesthetics vaporizers/respirators of the type Siemens Servo 900 C/D we found differences between the values adjusted at the instrument and those measured by the anaesthetic gas monitor (Sirecust 734 G). Control measurements yielded differences of inspiratory concentrations of halothane and isoflurane that were in excess by up to 80%. We found that the reason for this was the absence of reducing valves at the respirator that would reduce the static pressure of central gas supply from 5.3-5.5 bar to the values of not more than 4.0 bar that are permissible for the vaporizer. It is pointed out that the operation of respirators of this type is safe only provided the prescribed gas supply pressures are observed, if necessary with the help of the appropriate reducing valves, to ensure accurate dosage of volatile anaesthetics.